B12/Folate Problem set

Question 3: Effect of folate-B12 disruptions on neural membranes

Correct!

Which important enzyme cofactor, crucial to the integrity of neural membranes, is produced from methionine?

A.

homocysteine

B.

NADPH

C.

tetrahydrobiopterin

D.

S-adenosylmethionine

Perhaps a giveaway, since methionine is part of the answer! At any rate, S-adenosyl methionine (SAM, for short) is the critical link between the folate-B12 pathways and the neural symptoms produced when either pathway is disrupted. SAM is a crucial methyl donor for, among other things, the synthesis of phosphatidylcholine and sphingomyelin for neural membranes [Note that the lung, another tissue highly dependent on some of these same lipids, has a recycling pathway that does not require SAM.] Thus, the requirement of B12 for SAM formation is critical, but there is another part to the B12 story...